Field of the Invention
The invention relates to a monitoring method and device for signals for a localizer course transmission system.
Monitoring methods and devices are in normal use in instrument landing systems, since signals must be monitored in order to ensure that these systems are operating safely. It is thus known for the guidance signals which are transmitted via the localizer antenna from the localizer course transmitter to be checked to confirm that they are within specific, predetermined error limits.
In order to at least partially compensate for interference influences from relatively large reflective objects (for example hangars) at the side of the runway on the course signal received by an aircraft approaching the runway, it is known for a phase shift other than the conventional value of 0xc2x0 to be provided between the modulation signals for the course signal on the one hand and the clearance signal on the other hand so that, in one specific case for example, a phase shift of 94xc2x0 may be provided in order to take account of the abovementioned hangars for a specific runway. This is referred to as out-of-phase clearance.
The invention is based on the object of monitoring, in a simple manner, to ensure that such a phase shift is maintained.
One advantage of the invention is that the process of determining the phase shift means that any discrepancies, which may occur as a result of the errors occurring in the system or for reasons relating to maladjustment or incorrect operation can be detected quickly, in order that such discrepancies can then be compensated for. The method can be carried out in a particularly simple manner by joint use of those components (sensors and field dipole antennas, processors, digitizers etc.) which are already present in conventional monitoring devices, so that it leads to only minor additional costs.
It is particularly advantageous for the signals to be processed digitally by means of a digital processor.
Further features and advantages of the invention will become evident from the following description of an exemplary embodiment of the invention with reference to the drawing, which shows details essential to the invention. The individual features may each be implemented individually or in any desired combination of a number of them, in one embodiment of the invention.